This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. MRI/MRS has been shown to be a fast, safe and non-invasive method for measuring fat content in the liver and has proven to be an important tool for muscle lipid metabolism studies. Most of the prior studies on MRI/MRS of body fat have included only adults and to our knowledge no prior study has included the non-overweight pediatric population. This study will assess the liver and muscle fat content in healthy non-overweight children. Obtaining a range of normal values in healthy non-overweight children will aid in detection and evaluation of liver and muscle fat content in other diseases, such as in children with Cystic Fibrosis (CF). A prior study was performed at Children's Hospital of Philadelphia (CHOP) using MRI/MRS to assess liver and muscle fat accumulation in children with CF. One of the difficulties in interpreting the data is that normative data from healthy children of a similar weight and age is not available. The purpose of this study is to collect the normative data from healthy control subjects for comparison with the results obtained in patients with CF. In this study, healthy children 10 years or older will have their height and weight, and size of their waist, arms and legs skin fold thicknesses measured. An MRI/MRS of the liver and lower leg muscle will be performed. Body mass index (BMI) will be calculated. Hypothesis: Body fat measurements in normal weight children will differ from existing data in overweight children. The data for normal children is required for comparison with data from children with diseases such as cystic fibrosis.